Field of the Invention
Embodiments of the present invention relate generally to a multi charged particle beam writing method and a multi charged particle beam writing apparatus, and more specifically, relate, for example, to a beam irradiation method of multi-beam writing.
Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits becomes progressively narrower year by year. The electron beam writing technique, which intrinsically has excellent resolution, is used for writing or “drawing” patterns on a wafer and the like with electron beams.
As a known example of employing the electron beam writing technique, there is a writing apparatus using multi-beams. Since it is possible for multi-beam writing to irradiate multiple beams at a time, the writing throughput can be greatly increased in comparison with single beam writing. A writing apparatus employing the multi-beam technique, for example, forms multi-beams by letting portions of an electron beam emitted from an electron gun pass through a corresponding hole of a plurality of holes in a mask, performs blanking control for each beam, reduces each unblocked beam by an optical system, and deflects it by a deflector so as to irradiate a desired position on a target object or “sample”.
In multi-beam writing, the dose of each beam is individually controlled based on the irradiation time. Therefore, individual blanking mechanisms which can individually control ON/OFF of each beam are arranged in an array. If the number of beams increases, uncontrollable defective beams may be generated. For example, a continuous OFF beam which is unable to be emitted, and a continuous ON beam which is uncontrollable to be OFF are generated. If a defective beam is a continuous OFF beam, another beam can be a substitute to irradiate the target object surface. However, it is difficult to take measures for a continuous ON beam.
In order to solve this problem, there is proposed a method utilizing multiple exposure. For example, in M time exposures, one exposure is performed with a continuous ON beam (defective beam), and the remaining M-1 time exposures are performed with proper (normal) beams. However, since the continuous ON beam performs irradiation even during standby time for switching the beam to another pixel, the error of the irradiation time increases. In electron beam exposure, it is requested to perform dose control at the precision of about 0.1%. However, since exposure of multiple exposure is generally performed about eight times or sixteen times at most, even if the error of the irradiation time is equalized by the number of times, it is difficult to reduce the dose error to an allowable range.
As other countermeasures to the continuous ON beam, there is proposed a method of arranging blanking devices in two stages, in each of which a plurality of individual blanking mechanisms are arrayed, in order to block a continuous ON beam generated due to failure of one of the individual blanking mechanisms, by the other individual blanking mechanism (for example, refer to Japanese Unexamined Patent Application Publication (JP-A) No. 2013-197469). According to this method, it is necessary for the blanking device to include a large number of individual blanking mechanisms, each of which needs to have a control circuit. Therefore, the structure of the two-stage blanking device makes itself complicated and large.
Further regarding the multi-beam writing, there is proposed a method of dividing a shot of required irradiation time to irradiate the same position into a plurality of times of irradiation steps, and irradiating a target object continuously with the same beam in each irradiation step (for example, refer to Japanese Unexamined Patent Application Publication (JP-A) No. 2015-002189).